On west through north to east aspects at the higher elevations and on northerly aspects at the mid elevations new snow has been accumulating on slick or faceted old snow surfaces since Wednesday evening. In this terrain small to large slab avalanches could be human triggered on those old snow surfaces. Heavy snowfall accompanied by gusty southwest winds will be increasing the avalanche hazard in that terrain today. Monitor conditions and evaluate snow and terrain carefully. Avalanches are not likely in terrain where the recent new snow has accumulated on bare ground. These areas include all aspects below an elevation of 8,000 feet and southwest through south to southeast aspects up to an elevation of 10,000 feet.
At the upper elevations and on northerly aspects down to an elevation of 8,000 feet dense wind slabs could be human triggered in steep terrain on old snow surfaces. These slabs could be up to two feet deep and will be gaining depth and volume as the day progresses.
( Discussion is generated from the previous day's afternoon forecast. )The National Weather Service has issued a winter storm warning. The center of a low pressure system is moving down the west coast towards Seattle. As this system digs into northern California it will begin to direct Pacific moisture into the region. Moderate to heavy snowfall is expected to become widespread in the mountains on Friday and continue into Saturday. The freezing level is initially forecast to be around 6,500 feet and will lower as colder air moves in behind a cold front on Saturday. The mountains are expected to receive another 3 to 7 inches of new snow overnight and another 7 to 11 inches during the day on Friday. A mix of rain and snow is likely in the valleys. Temperatures in the mountains will be in the 20s tonight and will rise into the 30s during the day. Winds will be from the west-southwest at 18 to 22 miles per hour with higher gusts.The general avalanche hazard is expected to be MODERATE at the upper elevations (9,000 to 10,500 feet) on Friday and will be increasing as the day progresses. In steep terrain dense wind slabs one to three in depth could be human triggered on slick old snow surfaces. Avalanches are unlikely in areas where the recent new snow lies upon bare ground and on all aspects below an elevation of 8,000 feet.
